The present invention relates to a cylinder apparatus installed, for example, on a suspension system of an automobile.
Examples of cylinder apparatus installed on suspension systems of automobiles include hydraulic cylinders for vehicle height control and hydraulic dampers for shock absorption.
A known cylinder apparatus has a cylinder having a hydraulic fluid sealed therein; a piston sliding in the cylinder; and a piston rod connected at one end thereof to the piston. The other end portion of the piston rod projects from the cylinder. A seal block is provided between the piston rod and one end of the cylinder.
The seal block has a circumferential groove provided in the inner periphery thereof. A seal device is accommodated in the groove. The seal device has the form of a double seal including a seal ring engaged with the piston rod and an O-ring for pressing the seal ring against the piston rod.
This type of cylinder apparatus suffers from the problem that the O-ring is deformed by the pressure of hydraulic fluid in the cylinder, and this may cause the seal ring to engage the piston rod so strongly that the piston rod cannot smoothly slide.